High voltage generators for X-ray tube power supplies may comprise a multi-phase high voltage transformer which provides power for application to an X-ray tube cathode and anode. In typical prior art circuits an AC voltage adjusting device, for example an autotransformer, supplies line power to the multi-phase primary of a high voltage transformer. A switching device, for example a silicon controlled rectifier (SCR) in conjunction with a bridge rectifier, opens and closes the star point of the multi-phase primary to turn on and turn off high voltage at the X-ray tube. Inductive and capacitive effects in the transformer and associated power supply components generally cause the high voltage to rise above its steady-state level during a period immediately following completion of the circuit. The severity of this overshoot is known to increase with increasing X-ray tube voltage and to decrease with increasing X-ray tube current.
Turn on voltage overshoot in prior art X-ray generator circuits has been suppressed by the use of damping resistors. The use of such resistors is expensive both in terms of equipment cost and power consumption. Furthermore, the specific values of damping resistors used in a given X-ray generator must be tailored to the circuit parameters of that generator so that separate design and circuit production is required for each distinct generator circuit. The addition of overshoot supressing components to existing X-ray generators has, additionally, generally required the use of separate additional power supply circuits to operate active components in the overshoot supression addition and control lines to supply preset voltage and current information to the supression delay timer.